The present invention relates to splittable multicomponent fibers comprising starch and polymers and split fibers obtained from such splittable fibers. The present invention also relates to a process for making split fibers. The split fibers can have high elongation and can be used to make nonwoven webs and disposable articles.
There is a need for nonwovens that can deliver softness and extensibility. Soft nonwovens are gentle to the skin and are particularly useful in disposable products. Generally, decreasing fiber diameters can improve softness of nonwovens and other substrates. Nonwovens that are capable of high extensibility at relatively low force are also desired. These can be used to provide sustained fit in products and facilitate the use of various mechanical post-treatments. Typically, it has been found that having both small fiber diameter and high extensibility is difficult to achieve. This is because when the fiber diameter is reduced, it is commonly because the spinning speed or draw ratio has been increased which decreases extensibility of the fiber. Other ways to increase fiber extensibility of fine fibers include using higher-cost materials and or special mixing requirements.
There exists today a need for extensible nonwovens made with fine fibers that can be made with convention thermoplastic polymers, as well as for fibers that can be used to make such nonwovens and other substrates. The present invention can provide small diameter, extensible fibers in the form of split fibers obtained from splittable fibers splittable fibers that are cost-effective and easily processable. The splittable fibers are made of natural starches and thermoplastic polymers. The present invention also provides nonwoven articles and other substrates made from such split fibers.
The present invention is directed to splittable multicomponent fibers, to split fibers made from such splittable fibers, to a processes for making such splittable and split fibers, and to nonwovens and other substrates made from the split fibers. The splittable multicomponent fibers can comprise at least one nonencompassed segment of one component comprising thermoplastic starch and at least one nonencompassed segment of another component comprising a non-starch thermoplastic polymer, wherein: (i) said second component is capable of being split or removed from said first component to provide at least one split fiber consisting essentially of said first component; and (ii) wherein the split fiber of said first component has an Elongation to Break Ratio of greater than 1.0. As used herein, xe2x80x9cnonencompassed segmentxe2x80x9d means that the segment of the multicomponent fiber has at least one region of its lateral surface that is not encompassed by another segment of the multicomponent fiber. The splittable multicomponent fiber will produce at least one split fiber comprising the thermoplastic polymer, and can also produce a plurality of split thermoplastic polymer fibers. The splittable multicomponent fibers can also produce split fibers comprising the thermoplastic starch component. The split fibers corresponding to the thermoplastic polymer component will have a greater elongation than directly spun thermoplastic fibers which have an equivalent mass through put as the thermoplastic polymer component of the multicomponent fiber and which have the same diameter as the split fiber. This allows small diameter fiber to be produced at low spinning speed, so as to provide improved elongation properties, compared to conventional methods whereby cost effective processes run at high spinning speeds tend to result in poorer elongation properties, or wherein formation of small diameter fibers with good elongation are typically made according to processes with low mass through-put, and consequently low cost effectiveness.
The configuration of the splittable multicomponent fibers may be side-by-side, segmented pie, hollow segmented pie, islands-in-the-sea, segmented ribbon, tipped multilobal, or any combination of configurations. In general, segments will split or be splittable from adjacent segments of the fiber wherein the adjacent segment or segments constitute a different component of the multicomponent fiber.
The split fibers can be obtained from the multicomponent fibers hereof via chemical, mechanical, thermal, or other processes. Split fibers can also be obtained immediately upon formation of the multicomponent fiber, upon exit from the spinneret capillaries. The splittable nature of the fibers hereof is due at least in part to differences in rheological, thermal, solubility, surface energy, extensibility and/or solidification differential behavior between the components of the multicomponent fiber.
Without intending to be limited to any particular theory, it is believed that the splittable multicomponent fibers provide improved extensibility in the split fibers because they can be spun under conditions such that the fibers have relatively low molecular orientation and relatively large diameters. This can occur by using relatively slow spinning speeds, not subjecting the fibers to large drawing forces, and/or by increasing the through put per hole in the spinneret. Typically, fibers are drawn to smaller fiber diameters to increase the fiber strength and for a softer feel when used in a nonwoven. The drawing process, however, increases molecular orientation which results in a decrease in elongation to break of the fibers. Therefore, the split fibers of the present invention will have a higher elongation to break compared to fibers of the same diameter produced by direct spinning at equivalent mass through-put. In addition, the split fibers of the present invention can also have improved softness when used in a nonwoven fabric as a result of the improved extensibility.
The present invention is also directed to nonwoven webs and disposable articles comprising the split fibers. The nonwoven webs may also contain other synthetic or natural fibers blended with the split fibers of the present invention.